http://www.blume-religionswissenschaft.de/pdf/ReproductiveRe...
(PDF; p. 119, fig. 8.1)
Note that people who attend church/temple every week are well above replacement rate. The evolutionary race is on: those religious groups who manage best to transmit their "grow and multiply" gospel to their children will dominate demographics, and consequently politics, within our lifetimes.
I've never understood this.
A preference for large families seems logically unlinked to the primary evolutionary benefit of religious beliefs as I understand them: the cooperation level that is feasible when there is a powerful, omnipotent god to punish norm-violators.
Yes, religions which incorporate ideals about large families will tend to spread, but the same can be said about non-religious cultural memes.
And, in fact, shouldn't secular humanism (which stress the worth of people independent of their service to a god) be more compatible with large-family ideals than traditional religions (which stress duty to god over duty to self and others)?
EDIT: I read quickly though the paper you linked. It doesn't seem to answer my question. Rather it assumes the link between religion (belief in a judging god) and large-family ideals, and then arrives at the natural conclusion that religions are evolutionary advantages.
Or did I read it wrong?
The only such meme that ever had success comparable to religion was nationalism, but it self-destructed in the world wars.
Rationally speaking, I think it's well established that having kids is a huge chore. Morning sickness, birth pains, changing diapers, lack of sleep etc. etc. etc. If you had any doubt, the first baby will quickly cure you of it.
The only way for people to put up with all this, and raise large families, is to strongly believe, as you say, that they have an important _duty_ to do so. Giving birth for the benefit of the nation is no longer fashionable, but the various gods' appetite for fresh believers has never diminished.
By contrast, there is absolutely nothing in the world view of the "Sex and the City"-watching woman that will ever lead her to raise five kids.
Sure, but why aren't their such memes? I can imagine all sorts of hypothetical cultures which don't feature judging gods but do feature a duty to have children.
(By the way, how do you do italics on HN?)
A few people are partially or fully immune. (You don't have to be Mormon to be well off, educated and absolutely need to have 4+ kids) and over time their numbers will come to dominate.
I hope we've colonized space by then.
Trivial example: If an initial fraction f (with 0 < f < 1) of the population has a large growth rate of 5%/year and the rest of the population has a small negative growth rate of -1%/year, then the population as a function of time t in years is N[f(1.05)^t + (1-f)(0.99)^t]. For f = 1%, it takes less than a century for the growers to dominate the shrinkers: http://i.imgur.com/kv3KZ.png (blue is with f = 1%, red is f = 0%).